p–d hybridization, layered structure, and tetrahedral analysis in superionic conductors

The electronic states of silver halides and sodium halides are calculated by the DV-Xα cluster method to get microscopic evidence for the p–d hybridization in noble metal halides. It is found that both components of antibonding and bonding exist in the diagram of overlap population for AgX (X=halogen) and these two components are made up of the 4d band of Ag+ and the p band of halogen ion, which form the p–d hybridization. Next molecular-dynamics studies have been carried out on a model material which is composed of accumulating two different fluoride conductors: ⋯BaF2–CaF2–BaF2–CaF2⋯. The diffusion coefficient and ionic conductivity of F ions in the layered fluoride conductors increases with decreasing periods. These dependences coincide with experimental results. Lastly, the dynamical correlation between diffusing cations and tetrahedrons (THs) of the anion bcc sublattice in α-AgI is studied using molecular-dynamics simulations. When a Ag ion approaches the boundary surface of an empty marked TH, in which the Ag ion is not included, the area of boundary plane of the TH becomes larger in order for the Ag ion to go easily into the TH. THs repeat contraction and expansion with motion of mobile Ag ions.